This invention relates to a method of fabricating a micro-electromechanical systems device.
As set out in the material incorporated by reference, the Applicant has developed ink jet printheads that can span a print medium and incorporate up to 84 000 nozzle assemblies.
These printheads include a number of printhead chips. One of these is the subject of this invention. The printhead chips include micro-electromechanical components that physically act on ink to eject ink from the printhead chips.
The printhead chips are manufactured using integrated circuit fabrication techniques. Those skilled in the art know that such techniques involve deposition and etching processes. The processes are carried out until the desired integrated circuit is formed.
The micro-electromechanical components are by definition microscopic. It follows that integrated circuit fabrication techniques are particularly suited to the manufacture of such components. In particular, the techniques involve the use of sacrificial layers. The sacrificial layers support active layers. The active layers are shaped into components. The sacrificial layers are etched away to free the components.
Applicant has devised a new process for ma whereby two layers of organic sacrificial material can be used to support two layers of conductive material.
According to a first aspect of the invention, there is provided a method of fabricating a micro-electromechanical systems (MEMS) device that is positioned on a wafer substrate that incorporates drive circuitry, the method comprising the steps of
depositing a first sacrificial layer of an organic material on the wafer substrate,
patterning the first sacrificial layer,
depositing a first conductive layer of conductive material on the first sacrificial layer,
patterning the first conductive layer,
depositing a second sacrificial layer of organic material on the first conductive layer,
patterning the second sacrificial layer,
depositing a second conductive layer of conductive material on the second sacrificial layer,
patterning the second conductive layer, and
removing the sacrificial layers to release MEMS structures defined by the first and second layers of conductive material.
The method may comprise the steps of
depositing a third sacrificial layer of organic material on the second conductive layer,
patterning the third sacrificial layer,
depositing a structural layer of dielectric material on the third sacrificial layer, and
patterning the structural layer.
The steps of depositing the sacrificial layers may comprise spinning on layers of photosensitive polyimide.
The steps of depositing and patterning the sacrificial material and conductive material and removing the sacrificial material may be carried out so that the conductive material defines an actuator that is electrically connected to the drive circuitry.
The steps of depositing and patterning the sacrificial material, the conductive material and the dielectric material and removing the sacrificial material may be carried out so that the dielectric material defines at least part of nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber, the actuator being operatively positioned with respect to the nozzle chamber to eject ink from the ink ejection port.
According to a second aspect of the invention, there is provided a micro-electromechanical systems (MEMS) device that is the product of a process carried out according to the method described above.
In this specification, the device in question is a printhead chip for an inkjet printhead. It will be appreciated that the device can be any MEMS device.
In this specification, the term xe2x80x9cnozzlexe2x80x9d is to be understood as an element defining an opening and not the opening itself.
The nozzle may comprise a crown portion, defining the opening, and a skirt portion depending from the crown portion, the skirt portion forming a first part of a peripheral wall of the nozzle chamber.
The printhead chip may include an ink inlet aperture defined in a floor of the nozzle chamber, a bounding wall surrounding the aperture and defining a second part of the peripheral wall of the nozzle chamber. It will be appreciated that said skirt portion is displaceable relative to the substrate and, more particularly, towards and away from the substrate to effect ink ejection and nozzle chamber refill, respectively. Said bounding wall may then serve as an inhibiting means for inhibiting leakage of ink from the chamber. Preferably, the bounding wall has an inwardly directed lip portion or wiper portion, which serves a sealing purpose, due to the viscosity of the ink and the spacing between, said lip portion and the skirt portion, for inhibiting ink ejection when the nozzle is displaced towards the substrate.
Preferably, the actuator is a thermal bend actuator. Two beams may constitute the thermal bend actuator, one being an active beam and the other being a passive beam. By xe2x80x9cactive beamxe2x80x9d is meant that a current is caused to flow through the active beam upon activation of the actuator whereas there is no current flow through the passive beam. It will be appreciated that, due to the construction of the actuator, when a current flows through the active beam it is caused to expand due to resistive heating. Due to the fact that the passive beam is constrained, a bending motion is imparted to the connecting member for effecting displacement of the nozzle.
The beams may be anchored at one end to an anchor mounted on, and extending upwardly from, the substrate and connected at their opposed ends to a connecting member. The connecting member may comprise an arm having a first end connected to the actuator with the second part of the nozzle chamber walls and the roof wall connected to an opposed end of the arm in a cantilevered manner. Thus, a bending moment at said first end of the arm is exaggerated at said opposed end to effect the required displacement of the second part of the nozzle chamber walls and roof wall.